Double based diode



June 12, 1962 B. ROSS DOUBLE. BASED DIODE} Filed Sept. 26. 1955 IVLLNlLOd ATTORNEYS ilnited States 3,039,628 DQUBLE BASED DIODE Bemd Ross, Chicago, Ill., assignor to Hoffman Electronics Corporation, Los Angeles, Calif., a corporation of California Filed Sept. 26, 1955, Ser. No. 536,536 2 Claims. (til. 317-234) substance comprising atoms distributed in an integral part of the lattice structure of material.

semi-conductor material comprise atoms containing either a greater or lesser number of valence electrons than the constituent atoms of the intrinsic material. Where the atoms of the activating substance comprise more valence electrons than are associated with the atoms of the intrinsic material, the excess electrons may circulate freely in and through the crystal structure of the semi-conductor material and are hence available for electrical conduction purposes. Activating substances which provide excess electrons are commonly referred to as electron donors since they supply electrons which are free to move within the lattice structure of the semi-conductor material. Excess electron semi-conductors are commonly referred to as comprising N-type material since electrical conduction is carried on by the flow of negatively charged electrons through the material.

Where the atoms of the activating substance embody fewer valence electrons than are associated With the atoms of the intrinsic substance, each atom of activating material must borrow electrons from an adjacent atom of the intrinsic material thereby creating what may be referred to as a hole; that is to say, an incomplete group of atom bonding electrons simulating the properties of a positively charged electron in the lattice structure of the semi-conductor material. Hole creating activators Electrical energy may flow in either direction through both types of semi-conductor material. When, however, a body of P-type material is joined with a body of N-type material to form therebetween what is commonly referred to as a P-N junction, the positive holes in the P-type material and the free electrons in the material are mutually repelled away In this connection, the P-N junction is the equivalent of a unidirectional potential source having a negative side and positive sides respectively connected with the P-type and N-type materials on opposite sides of the junction, thereby constituting the junction as a potential hill, past which electrical energy may fiow more easily in one direction than the other. If, for example, the opposite positive and negative sides of a source of unidirectional atent assaszs Patented June 12, 1962 thee electrical potential be connected respectively with the N-type and P-type ends of a P-N junction element, in fashion commonly referred to as reverse bias, such potential source will merely increase the potential hill, by drawing the valence electrons and holes mutually away from the junction, and, consequently place across the P-N junction. nection of the positive and negative sides of a source exceeds the potential drop across the junction element, including the equivalent potential value of the junction hill. Accordingly, a semi-conductor element embodying a P-N junction may be employed as an electrical power rectifier.

Heretofore semi-conductor elements embodying P-N for example, to thereby constitute the resulting crystalline substance as -type semi-conductor material. Thereafter growth of the crystal ingot may be continued kind, acceptor material, constitute the subsequently portions of the ingot as P-type material. In such an ingot, the P-N junction extends between the N-type and P-type portions of the ingot body.

A so-called double based diode may comprise bodies of P-type and N-type material inter-connected by means of a P-N junction, provision being made for the ohmic connection of one of said bodies in an external circuit at spaced apart contact stations, called bases, on said body, and for the ohmic contact of the other of said bodies in external circuitry, in order that the device may function in desired as hereinafter described.

like zone on the disc.

Another important object is to atomic penetration of the substance within the material of the plate at and inwardly of a surface thereof, to thereby produce a P-N junction within the body of the plate between such substance penetrated portions of the plate and the plate material inwardly of said portions.

Another important object is to provide a device of the chaacter mentioned by first forming a body of crystalline semi-conductor material of desired configuration and selected type and thereafter exposing the body in an atmosphere comprising a vaporized activating substance of another type, to obtain penetration of such substance to a desired depth beneath the exposed surface of said body to thereby form a P-N junction between the so penetrated portions of said body and the material thereof inwardly of such penetrated portions, thereafter removing some of the so penetrated portions to thereby retain only desired parts on zones thereof on the body, while exposing material of the body to which the activating substance has not penetrated, in order to define the marginal edges of said zones, and also to permit ohmic contact with said unpenetrated body portions at contact stations spaced from the P-N junction.

Another important object is to provide an ohmic contact on a device of the character mentioned embodying integrated body portions providing a P-N junction therebetween, by exposing the device in an atmosphere comprising a vaporized conditioning substance to obtain penetration thereof to a desired depth at and beneath the surfaces of at least one of said body portions to thereby provide ohmic contact therewith, thereafter removing some of the so penetrated surface portions to a depth greater than the penetration of the conditioning substance whereby to isolate and localize the zone of ohmic contact.

Another important object is to provide a semi-conductor device of the character mentioned by first forming a body of crystalline material doped with activating material of desired type, thereafter exposing the body in an atmosphere comprising a vaporized activating substance of another type, to obtain penetration of such substance to a desired depth, at and beneath the surface of said body, and to produce a P-N junction between the penetrated and impenetrated portions of said body, there after removing surface portions of the body to a depth greater than the penetration of such activating substance, to thereby define the marginal edges of an activated zone in said body, and to expose body material, around said zone, to which the activating substance has not penetrated, and by thereafter applying a vaporized medium to such exposed body portions to provide an ohmic contact zone on said body.

Another important object is to provide a semi-conductor device of the character mentioned comprising body portions of material of unlike type providing a P-N junction therebetween, one of said bodies having an ohmic contact zone formed thereon remote from said junction and a metal wire integrally connected to said body and forming another ohmic contact zone remote from said junction; a further object being to apply the metal wire on the body by heating the same and the wire to a temperature approaching the melting temperatures of the material of the body and wire, and by thereafter pressing the wire into the body to a desired depth to thereby accurately determine the spacement between the embedded end of the wire and said P-N junction.

Another important object is to provide a semi-conductor device of the character mentioned comprising a relatively thin plate of material, such as silicon, containing an activating substance constituting the plate as a semi-conductor of desired type, means forming a body of material of different type on said plate to provide a P-N junction between said body and plate, and means forming ohmic contact with said plate comprising a wire of metal, such as gold, containing an activating substance to constitute the metal wire as material of type like that of the body, the wire it an end thereof being embedded in and thus integrally connected with the plate.

Another important object is to provide a semi-conductor device of the character mentioned comprising crystalline material, such as silicon, containing an activating substance to constitute the plate as a semi-conductor of desired type, the plate having a surface portion doped with a different activating substance to a desired depth to constitute the doped portions of the plate as a semi-conductor of type different from that constituting the remaining portions of the plate; a further object being to form bases.

on said remaining portions of the plate a pair of ohmic contact zones or stations, constituting a pair of contact bases on said device.

Another important object is to provide a semi-conductor device of the character mentioned comprising a plate of silicon containing an activating substance to constitute the plate as an N-type semi-conductor, the plate having a surface portion doped with an activating substance such as boron to a desired depth inwardly of the surface to thereby constitute the doped portions of the plate as P-type semiconductor material, the plate, remote from said doped portions, being treated as with excess electron donor material, such as phosphorus, to form an ohmic contact zone on the plate remote from said doped portion, as at the peripheral edges of said plate, and a wire of material such as gold, containing antimony or other suitable electron donor material atornically dispersed therein, said wire having an end integrally connected in said plate form ohmic contact therewith in position spaced from said doped portion.

The fore-going and numerous other important objects, advantages and inherent functions of the invention will become apparent as the same is more fully understood from the following description, which, taken in connection with the accompanying drawings, discloses preferred embodiments of the invention.

Referring to the drawings:

FIG. 1 is a purely diagrammatic illustration of a double based diode structure for the purpose of revealing the manner in which such devices are adapted to function;

FIG. 2 is a perspective view of a double based diode made in accordance with the teachings of the present invention;

FIG. 3 is an enlarged sectional view taken substantially along the line 33 of FIG. 2;

FIGS. 4 and 7 are sectional views taken through modified double based diodes made in accordance with the teachings of the present invention;

FIG. 5 is a graphical representation of the potential radient which may be established radially outwardly in the diode shown in FIG. 4 when the same is in operation; and

FIG. 6 is a greatly enlarged sectional view showing portions of the device illustrated in FIG. 3.

To illustrate the invention, FIG. 1 of the drawings diagrammatically illustrates the functional parts of a double based diode 11, the same comprising a body 12 of semi-conductor material of selected type, the body 12 being provided with ohmic contact means 13 and 14 forming spaced apart bases at the opposite ends of the body 12. A conventional double based diode of the sort illustrated in FIG. 1 may also include a body portion 15 of material of type unlike that of the body 12, the bodies 12 and 15 being integrally connected to form a P-N junction 3' therebetween.

By inter-connecting the bases 13 and 14 with a power source B such as a battery providing electrical potential of V volts, the potential at any zone or level such as the level C, in the body 12 between the bases 13 and 14, will be proportional to the distance of such level from one of the bases, such as the base 13, as compared with the distance between the bases, the material of the body 12 providing substantially uniform resistance between the If it be assumed that the level C is precisely midway between the bases, then the electrical potential at the level C with respect to either base will be V/Z. If an equivalent potential be applied between the base 13 and the body portion 15, as by means of a power source S, the entire junction surface I, on the side thereof which faces the body portion 15 will be at potential V/ 2, while the potential on the opposite side of the junction will be equal to V/2 only at the level C. All portions of the junction I above the level C, on the side of the junction which faces the body 12, will be at a potential greater than V/2, while all portions of the junction below the level C, on the side of the junction which faces the body portion 12, will be at a potential less than V/2. Accordingly the junction portions below the level C may be electrically biased in the forward direction so that electrical current will be urged to flow from the body portion through the junction and into the body portion 12. Above the level C, however, the junction will be electrically biased in a direction tending to cause current flow from the body 12 to the body portion 15, but such current fiow may not take place, because of the rectifying action of the diode structure at the P-N junction. Current flow through the junction below the level C may cause the emission of holes into the material of the body 12, thereby lowering its resistance between the bases 13 and 14. As a consequence, current flow through the body 12- between the bases 13 and 14, under the influence of the battery B, will increase, thereby shifting the potential level C toward the base 14. Accordingly, a larger junction area, beneath the so shifted level C, will be made available for current flow from the body 15 into the body 12, thereby further reducing the resistance of the body 12 between the bases 13 and 14. The foregoing shift in potential level on the side of the junction which faces the body 12 will continue until the potential level registers with that edge of the junction which is closest to the base 14. The foregoing characteristic phenomenon constitutes the double based diode as the equivalent of a resistor having negative resistance characteristic since, without change in applied potential, current how has increased.

The present invention has, for its important object, the provision of a double based diode of novel construction, the same, as shown, for example, in FIGS. 2, 3, 4, 6 and 7, preferably comprising a disc or plate of a suitable semiconductor material, such as silicon, forming the body 12 of the diode, the material of the body containing a selected activating substance distributed through the lattice structure of the material in order to provide the body with desired semi-conductor characteristics. Atomic quantities of the activating substance may thus be distributed through the body 12 in the proportions of one atom of activating substance for every 100,000,000 atoms of its intrinsic material. Arsenic, antimony or other suitable electron donor material may thus be employed as an activating substance in order to constitute the material of the body 12 as N-type semiconductor material, while boron, indium or other suitable acceptor material may be employed as an activating substance if it be desired to constitute the body 12 as a P-type semi-conductor.

The body 12 preferably comprises a relatively thin disc or plate, which may be cut from a crystalline ingot of the selected semi-conductor material containing a desired activating substance. Portions 16 of the plate, at and inwardly of a surface thereof, may be treated with an activating substance, other than and difierent from that distributed in the body 12, in order to alter the type of the semi-conductor material at and to a desired depth inwardly, of the bounding surface of the treated portions 16. Where the plate which forms the body 12 comprises N-type semi-conductor material, the portions 16 may be treated with boron, aluminum, indium or other electron acceptor substance in order to constitute the plate portions 16 as P-type semi-conductor material. Conversely, Where the material of the body 12 comprises P-type semiconductor material, the portions 16 may be treated with arsenic, antimony or other electron donor substance in order to constitute the portions 16 as N-type semi-conductor material. Preferably, the body 12 comprises N- type silicon embodying arsenic or antimony as the activating substance, the surface portions 16 being treated with boron in order to constitute the same as P-type semiconductor material.

The activating substance, employed to determine the character of the material in the portions 16, may be applied to the surface of the plate and caused to penetrate to a desired depth therein by exposing the plate 12 in an atmosphere consisting of the activating substance in its vaporized condition, the plate 12 being retained in such atmosphere and hence soaked in the vaporized activating substance during a period sufficient to obtain penetration of the activating substance to a desired depth at and beneath the surface of the plate. Any suitable preferred or convenient means may be employed to prevent the application of the activating substance to other surface portions of the body 12 than those at which penetration of the activating substance is desired. It is, however, preferable to expose all plate surfaces to the vaporized activating substance so that penetration of the activator is obtained at all exposed surfaces of the plate. Thereafter, the plate may be ground, milled, etched or otherwise worked or recessed as at 17 in order to remove all surface portions of the plate that have been penetrated by the activating substance except those portions 16 which it is desired to retain. A suitable etching medium for such purpose may comprise a mixture of nitric and hydrofluoric acids. As shown, the present invention contemplates retention of a referably ring-like zone forming the treated portions 16, such Zone being disposed concentrically in the disc forming the body 12. If desired, however, the portions 16 may be formed as a plate-like zone, at the center of the disc, as distinguished from the rin -like zone configuration illustrated. it will be apparent, of course, that a P-N junction will be established between the activated portions 16 and the remaining or underlying portions of the body 12.

After formation of the activated surface portions 16, means may be formed on the body 12 to provide ohmically connected bases 13 and 14 thereon. To this end the plate 12, if it comprises N-type semi-conductor material, may be exposed to the action of vaporized phosphorus or other especially active electron donor material, in order to constitute the remaining surface portions 18 of the plate 12., as for example, the surface portions disposed, in the plate, outwardly of the activated portions 16, as N+ type semi-conductor material, to a desired depth. Where the constituent material of the plate 12 comprises P-type semi-conductor material the plate should, of course, be treated with an especially active electron acceptor substance in order to form P+ type material in the plate portions 18.

After the character of the material in the plate portions 18 has been established, to a desired depth, to form ohmic connection with the body portions of the plate 12, the plate may be ground, milled, etched or otherwise worked or processed, as at 19, in order to isolate the activated material comprising the portions 18 from the material constituting the portions 16. As shown, the retained portions 18 may be of ring-like configuration and may be disposed at the marginal edge of the plate 12, the inner edge of the retained portions 18 @being equally spaced from the outer edge of the portions 16. Exposure of previously in activating the portions 1 8 will not materially alter the character of the portions 16. If desired, however, the exposed surfaces of the portions 16 may be coated or otherwise masked by means of a layer of material which is impervious to the activating substance, during exposure of the portions 18 to said activating substance.

In order to protect and also to provide for electrical connect-ion of the activated portions 16 and 18 in external electrical circuits, said surfaces may be provided with a coating of nickel 2%), which may be applied in any suitable or convenient fashion as by electro-deposition of the material, or by condensing it upon the surfaces to be coated from a vaporized atmosphere of the coat-ing material. The application of such a coating layer to the surface of the portions 16, prior to the application of an activating substance to the portions 18, will, of course, preclude any contamination of the portions 16 by the substance applied to activate the portions 18.

In the embodiments illustrated in FIGS. 2, 3 and 4, the base connection 13 may comprise an alloyed junction 21 formed by connecting a length of metal wire 22 doped with an activating substance to constitute the wire as material of the same type as that of the body 12. Where the body 12 comprises N-type silicon the wire 22 may comprise gold, or other suitable metal, doped with antimony or other preferred electron donor material. The wire 22 may be attached to the plate 12 by heating the plate and the wire to a temperature of the order of, but somewhat less than, their melting temperatures, and by then pressing the end of the wire upon and into the plate to a selected depth at the place where it is desired to form the junction. As the end of the wire becomes alloyed with the material of the plate, it will spread and expand to a limited extent, as shown, and the alloyed junction 21 of ohmic character will be formed between the plate and the Wire, said junction comprising recrystallized material of the plate containing the material of the wire disposed therein. The connection wire 22 is preferably applied in position disposed concentrically with respect to the treated portion 16 so that the edge of the treated portion 16 and of the P-N junction J is substantially equidistant from the ohmic junction 21 in all direction radially of the wire 22. The wire 22 as shown in FIGS. 2 and 3 may be connected to the same side of the plate 12 upon which the portions 16 and 18 are formed. However, as shown in FIG. 4, the wire 22 may be attached to the side of the plate 12 opposite from that upon which the treated portions 16 are formed. It is also within the contemplation of the invention to apply a ring-like junction forming portion 16, an ohmic junction 18 and an ohmically connected wire 22, on both of the opposite sides of the plate.

As shown more particularly in FIGS. 4 and 7, the ohmic connection portions 18 which form the base 14, may extend peripherally of the plate 12-on both sides of and across the marginal edge of the plate, such arrangement being particularly desirable where the ohmic connection 13 is disposed on the side of the plate remote or opposite from the treated portions 16, or Where a junction forming portion 16 and ohmic connection 13 are formed on each of the opposite sides of the plate. Furthermore, as shown more particularly in FIG. 7, the ohmically connected base 13 may comprise a body portion 18' of character identical to the body portions 18, the portions 18 and 18 being formed simultaneously in the surfaces on the plate 12 and being defined and separated by the removal, as at 19', of intervening treated portions of the plate 12.

In making the devices shown in FIGS. 2, 3, 4 and 7, the plate 12 may first be exposed to vaporized material for conditioning the portions 16. Activated surface portions of the plate may then be cut away as to the level 17 to remove all treated portions except those that it is desired to retain in the finished diode. Thereafter the plate may be exposed to the fumes of an activating substance for conditioning the plate portions 18 and 18. The plate may then be coated as with nickel to form the layers 20, after which the material of the treated and coated plate may be cut away, as at 19, to leave only such portions of the layers 16, 18 and 20 as may be desired to retain. In the embodiment shown in FIG. 7 the portions 18 and 18 and their covering layers will be formed simultaneously in the diode. In forming the devices shown in FIGS. 2, 3 and 4, the wire 22 may be attached as the concluding step in the production of the diode.

The foregoing procedure for the fabrication of a double based diode allows for exceedingly precise control of the spacement of the ohmically connected bases 13 and 14 with respect to the P-N junction I. It also allows the area of the junction I to be controlled easily and with utmost precision. Diodes may be made in accordance with the present invention in any desired size limited only by mechanical ability to produce and work the plate 12 of intrinsic material. In that connection, diodes having a diameter of as little as Ms inch and as large as one inch and more are entirely feasible, the power transferring ability of the device, of course, being a function of its physical size.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the forms herein disclosed being preferred embodiments for the purpose of illustrating the invention.

The invention is claimed as follows:

1. A semiconductor device comprising a body of semiconductor material of relatively thin fiat shape presenting opposed major surfaces, a central ohmic contact zone on one of said surfaces, a rectifying junction contact of annular configuration on the other of said surfaces, disposed about and spaced in the axial direction away from said central contact zone but inwardly of the margins of said body, said rectifying junction contact forming a gate electrode contact, and a second ohmic contact zone constituted by contact material formed upon the peripheral margins of both said major surfaces of said body and extending integrally across the edge thereof; said two ohmic contact zones forming source and drain electrodes adapted for connection with an external load circuit for control of the current flow therein in accordance with the electric field established by said junction contact transversely of the internal load circuit between said ohmic contact zones.

2. A semiconductor device comprising a body of semiconductor material of relatively thin flat shape presenting opposed major surfaces, a central ohmic contact zone on one of said surfaces, a rectifying junction contact of annular configuration on the other of said surfaces, disposed about and spaced in the axial direction away from said central contact zone but inwardly of the margins of said body, said rectifying junction contact forming a gate electrode contact, said body additionally carrying ohmic contact material on the peripheral margins of both of said major surfaces of said body outwardly of said annular junction contact, and means electrically connecting the ohmic contact material on said peripheral margin portions to define therewith a second ohmic contact zone; said two ohmic contact zones forming source and drain electrodes adapted for connection with an external load circuit for control of the current flow therein accordance with the electric field established by said junction contact transversely of the internal load circuit between said ohmic contact zones.

References Cited in the file of this patent UNITED STATES PATENTS 

